KR101162778B1 - Method for making brazed heat exchanger and apparatus - Google Patents

Abstract

A heat exchanger having a boiling passage and a cooling passage formed by opposite sides of a metal wall is disclosed. The layer of brazing material between the metal wall and the spacer member joins the components of the heat exchanger together. An enhanced boiling layer (EBL) comprising metal particles bonded to each other and to the boiling side of the metal wall provides nuclear boiling pores to enhance heat transfer. EBL has a melting temperature higher than the melting temperature of the brazing material. Also disclosed is a process of assembling a heat exchanger.

Description

METHOD FOR MAKING BRAZED HEAT EXCHANGER AND APPARATUS}

The present invention relates to an improved method of manufacturing a metal heat exchanger with high heat transfer efficiency. In particular, the present invention relates to an improved method of manufacturing a brazing heat exchanger comprising an enhanced boiling surface.

Currently, two configurations of heat exchangers are generally used for reboiler-condensers in cryogenic, purification and chemical applications. One type of heat exchanger currently in use is a vertical shell and tube heat exchanger. In this configuration, enhanced boiling layers (EBLs) are used to obtain sufficiently high heat transfer at relatively low temperature differences. EBLs usually have a structure that includes a plurality of pores that provide for boiling nuclear sites to facilitate boiling. The EBL is attached to the inside of the tube and is provided with a longitudinal groove on the outside of the tube to facilitate heat transfer.

An enhanced boiling layer was first proposed in the heat exchanger in US Pat. No. 3,384,154. This patent discloses mixing a metal powder with a plastic binder in a solvent and applying the slurry to the base metal surface. The coated metal is heated to a predetermined temperature for a sufficient time in a reducing atmosphere, so that the metal particles are sintered together on the base metal surface. U. S. Patent No. 3,457, 990 discloses an enhanced boiling surface in which recesses are formed mechanically or chemically therein.

Other methods of attaching EBLs are disclosed. British Patent No. 2 034 355 discloses attaching an organic foam layer to a metal heat transfer member and plating the foam layer with a metal such as copper first by electroless plating and then by electroplating. U.S. Patent 4,258,783 discloses mechanically forming recesses in the heat transfer surface and then electroplating the metal on the recessed surface. British Patent 2 062 207 discloses attaching metal particles to a metal base by powdered flame spraying. EP 303 493 discloses spraying a mixture of metal and plastic material onto a base metal by flame or plasma spraying. U.S. Patent No. 4,767,497 and U.S. Patent No. 4,846,267 disclose heat treating an aluminum alloy plate to produce a precipitate and chemically etching the precipitate to leave a concave surface. EP 112 782 discloses applying a mixture of brazing alloy and spherical particles to a metal wall and heating the coated wall to melt the brazing material.

Common heat exchangers used for cryogenic, refining and chemical applications are plate-fin brazed aluminum heat exchangers made by placing corrugated aluminum sheets between aluminum separating sheets or walls to form a plurality of flow paths. The sheet is inserted between the surfaces to which the aluminum brazing layer is to be coated or to which the brazing foil layer is to be bonded. When heated to a predetermined temperature for a predetermined period of time, the brazing foil or cladding melts to form a metallurgical bond with adjacent sheets. The resulting heat exchanger includes a plurality of passages consisting of alternating layers of closely spaced fins. Conventional structures of alternating layers of passageways that each receive fins have a density of 6 to 10 fins / cm (15 to 25 fins / inch) and a fin height of 0.5 to 1 cm (0.2 to 0.4 inches). In a typical application, a series of first alternating passages carries a condensation vapor and a series of second alternating passages carries a boiling liquid. Conventional brazed aluminum heat exchangers must be able to withstand 2068-2758 kPa (300-400 psia).

Patents suggesting replacement of fins with reinforced boiling layers in the boiling passages of brazing heat exchangers include US Pat. Nos. 5,868,199, 4,715,431 and 4,715,433. These patents suggest stacking aluminum sheets, with one side of each aluminum sheet attached with an EBL to form a boiling channel and the other side with fins to form a condensation channel. A brazing material layer is disposed between the joining surfaces in the stack and the stack is heated over a period of time to obtain a brazing heat exchange core. Such brazed aluminum heat exchangers disclosed in these patents have not been commercialized and EBLs are typically brazed at 565 ° C to 593 ° C (1050 ° F to 1100 ° F), while subsequent brazing of the metal components is about 593 ° C to 621 ° C (1100 ° F). To 1150 ° F.). During the high temperature second heat treatment for carrying out the brazing, maintaining the integrity and effectiveness of the EBL, in particular the pore structure provided by the interbonded metal particles, was difficult. This difficulty causes the absence of a commercially available brazing heat exchanger with EBL in the boiling passage.

The present invention relates to an improved method and resulting apparatus for manufacturing a brazed metal heat exchanger. An enhanced boiling layer (EBL) is provided on the wall of the boiling passage. The melting temperature of the brazing material is lower than the melting temperature of the metal particles in the enhanced boiling layer. In an embodiment, the metal of the enhanced boiling layer and / or brazing layer is an alloy of the first metal and the second metal, which alloy has a lower melting temperature than the first metal. Other second metals can be used in the EBL and brazing material as long as the second metal lowers the melting temperature of the alloy. In an embodiment, the concentration of the second metal in the brazing material is greater than in the EBL. Thus, it has been found that even for a prolonged period of time, even if the brazing temperature is within 8.3 ° C. (15 ° F.) of the melting point of the metal in the EBL, the EBL unexpectedly maintains its porosity and thus its efficiency. In an embodiment, the condensation passage includes fins to facilitate heat transfer.

It is an object of the present invention to provide a metal heat exchanger having an EBL in the boiling passage which does not reduce its heat transfer capacity even at brazing temperatures during manufacture.

1 is a perspective view of three heat exchangers;

2 is a perspective view of the core of the heat exchanger of FIG. 1 with the layer broken to reveal the interior;

3 is a perspective view of the heat exchanger core of FIG. 1, but taken in a different perspective from FIG. 2; FIG.

The method of the present invention can be used to construct any form of heat exchanger by brazing, including shells and tubes, but is most appropriately applied to plate heat exchangers. The boiling and cooling passages of the heat exchanger of the present invention may be oriented to provide cross flow, counter-current flow or cocurrent flow. The heat exchanger of the present invention may also be applied to any other process situation that relies on boiling to effect cryogenic air separation, hydrocarbon treatment or heat exchange. Several types of metals can be used to construct the heat exchanger. In brazed heat exchangers, aluminum is the most widely used metal. Aluminum is suitable for cryogenic applications because it resists brittleness at low temperatures. Steel or copper may be used to heat or cool a fluid that may be corrosive to aluminum. For illustration purposes, the present invention will be described with reference to a countercurrent aluminum plate heat exchanger useful in cryogenic air separation situations.

1 illustrates the heat of a conventional plate heat exchanger 10 used for cryogenic air separation. In the heat exchanger 10, alternate boiling passages 12 and cooling passages 14 are provided in the core 20. Liquid, such as liquid oxygen, is carried to the manifold 18 by the conduit 16 and distributed to the boiling passage 12. The transport of the liquid below the core 20 to the boiling passage 12 by means other than the conduit 16 or the manifold 18 is, for example, by thermosiphon at the bottom of the boiling passage 12. It is expected. Also, liquid may be transported to the boiling passage 12 from the side or top of the core 20 via a distribution network, which may be provided with a distribution pin. The liquid boils in the boiling passage 12, thereby indirectly withdrawing heat conducted from the cooling passage 14. Vapor phase oxygen from the boiling passage 12 is collected by the header 22 or the like and removed through the conduit 24. Gas collection from the boiling passage 12 is envisaged by means other than the conduit 24 or header 22 above the core 20, as may be provided in the thermosiphon structure. In addition, gas may be collected in the boiling passage 12 from the side or top of the core 20 via a collection network, which may be provided with collection pins. Conduits 26 carry fluid such as gaseous nitrogen to manifold 28 and distribute it to cooling passage 14. Delivery by means other than conduit 26 or manifold 28 is also contemplated. Liquid or gas may be cooled in the cooling passage 14. Moreover, when the gas is delivered to the cooling passage 14, the gas can be cooled to a range such that a phase change occurs with or without a temperature change, depending on the necessity of the process. The heat conducted across the wall between the cooling passage 14 and the boiling passage 12 to assist boiling in the boiling passage 12 cools the fluid in the cooling passage 14, thereby providing nitrogen gas in the case of air separation. To condense. Fluid such as liquefied nitrogen from the cooling passage 14 is collected by the header 30 or the like and removed through the conduit 32. The collection of the cooled fluid from the cooling passage 14 by means other than the header 30 and the conduit 32 is expected. In addition, the transport and collection manifolds and conduits shown in the embodiment of FIG. 1 may be modified and maintained within the scope of the present invention.

FIG. 2 shows the core 20 of one of the heat exchangers 10 partially broken to reveal the interior. Cap ends 40 are disposed at both ends of the core 20 to form the last channel on each end. A portion of the cap seat 40 shown in FIG. 2 is broken to reveal the boiling passage 12. A vertical spacer bar or spacer member 42 is disposed between the opposite edges of the cap sheet 40, and the metal wall 44 with the boiling side 44a is covered with a reinforced boiling layer (EBL) 46. EBL 46 includes thermally conductive particles that are bonded to each other and to the boiling side 44a to form a pore structure in which a nuclear boiling site is provided. The thermally conductive particles are metal particles in the examples. Thus, the boiling passage 12 is formed by the inner surface of the cap sheet 40, the inner edge of the vertical spacer bar 42 and the boiling side of the metal wall 44. The outer vertical edge 48 of the boiling side 44a is devoid of EBL 46 at all to provide a bonding surface. Vapor may exit the boiling passage 12 through the boiling outlet 49 and may be collected by the boiling header 22 shown in the embodiment of FIG. 1. It is also contemplated that the boiling passage 12 may comprise fins to further facilitate heat transfer. At the back of the broken metal wall 44 and the vertical spacer bar 42 is a cooling passage 14 comprising a primary fin 52 having a corrugated sheet of primary fin stock 54. The primary fins 52 extend laterally between the inner edges of the vertical spacer bar 42 at both ends of the cooling passage 14. Dispensing pins 56, which include or are integrated with primary pin stocks 54, are disposed in an inclined fashion to provide cooling fluid from cooling inlet 50 by primary fins 52. Distribute evenly along the top of the. In the embodiment of FIG. 2, cooling fluid is received into the cooling inlet 50, which may exit from the cooling manifold 28 as shown in the embodiment of FIG. 1. Other types of dispensing arrangements with or without pins may be used to dispense the cooling fluid. In other embodiments, the cooling inlet 50 may take into account the top of the channel provided by the primary fins 52. To illustrate the top of the primary pin 52, only one set of distribution pins 56 is shown in FIG. 2. The cooling outlet 64, which may be formed by the collecting pin 66, causes the cooled fluid to exit the core 20. In the embodiment of FIG. 2, the cooling fluid is discharged through a cooling outlet 64 that can enter into the cooling header 30 in the embodiment of FIG. 1. Horizontal spacer bar 60 seals the top and bottom of the cooling passage 14. Spacer bars 42, 60 and fins 52, 56, 66 space the cooling side 44b (opposite side) of metal wall 44 from the cooling side 44b of adjacent metal wall 44. In an embodiment, no horizontal spacer bar 60 is provided in the boiling passage 12 to enable inflow and discharge of fluid into and out of the boiling passage 12 respectively. Thus, vertical spacer bars 42 are sandwiched between opposing ends of each pair of adjacent metal walls 44, while horizontal spacer bars 60 are sandwiched only between adjacent cooling sides 44b. However, it is contemplated that the spacer bars 42, 60 can be omitted between the cooling sides 44b of the cooling passage 14 if the fins 52, 56, 66 are arranged and joined to adequately withstand the operating pressure. . Thus, pins 52, 56, 66 provide a spacing function. The metal wall 44 has an alternating orientation. Except when adjacent to the cap seat 40, the cooling side 44b of the metal wall 44 always faces the cooling side 44b of the adjacent wall, and the boiling side 44a of the metal wall is always adjacent metal. It faces the boiling side 44a of the wall 44. In addition, in the embodiment, it is expected that the cooling passage 14 does not include fins and that the fins are provided in the boiling passage 12.

3 illustrates the core 20 of FIG. 2 in perspective showing the bottom of the core 20. All elements of FIG. 2 that can be seen in FIG. 3 are numbered. Also shown is a boiling inlet 51 for the boiling passage 12. In an embodiment, the boiling inlet 51 may receive boiling liquid from the boiling manifold 18 (FIG. 1). Moreover, the bottom of the cap seat 40 and the first metal wall 44 are broken to reveal the collecting pin 66 from the third pin stock 68. The collecting pins 66 having a third pin stock 68 or integrated with the primary pin stock 54 are arranged in an inclined manner and along the bottom of the channel provided by the primary pins 52, the cooling outlet 64. Collect the cooling fluid uniformly). Other types of collection configurations may or may not be used to collect cooling fluid. In other embodiments, the cooling outlet 64 may take into account the bottom of the channel provided by the primary fins 52. To illustrate the bottom of the primary pin 52, only one set of collection pins 66 is shown in FIG. 3.

On the boiling side, the EBL is added by any method known in the art, such as slurry application, flame spraying, plasma spraying or electroplating. However, once attached, it is important that subsequent brazing steps do not reduce the heat exchange efficiency of the EBL. In an embodiment, the melting point of the EBL is higher than the melting point of the brazing metal. The relative melting point of the brazing metal and the EBL can be achieved by alloying the first metal and the second metal with the effect of providing a melting point of the alloy lower than the melting point of the first metal. The concentration of the second metal can be higher in the brazing metal than in the EBL material, so that the EBL has a higher melting point that can withstand the brazing step without losing structural integrity. In a brazing aluminum heat exchanger, aluminum may be the first metal and silicon, manganese, magnesium or their alloys may be the second metal. In a brazing steel heat exchanger, nickel may be the first metal and phosphorus may be the second metal. In a brazing copper heat exchanger, copper may be the first metal and phosphorus may be the second metal.

In the case where the copper is the first metal used to provide the EBL and the brazing material, the brazing occurs at 100 ° C. (180 ° F.) below the melting temperature of the copper or at 960 ° C. (1760 ° F.). If aluminum is the first metal, brazing occurs at temperatures between 49 ° C. and 54 ° C. (120 ° F. to 130 ° F.) below the melting temperature of 649 ° C. (1200 ° F.). If nickel is the first metal, the brazing step in the furnace takes place at a temperature of 1037 ° C. (1900 ° F.) which is 38 ° C. (100 ° F.) below the melting temperature of the steel. At these temperatures, the second metal, together with the first metal, lowers the melting point of the alloy. The liquefied brazing metal flows and diffuses into the base metal to form a metallurgical bond. By alloying more second metal with the first metal in the brazing material than in the EBL material, the EBL once attached can withstand subsequent lower temperature brazing heat treatment.

It is also envisaged that sintering can be used to form EBL instead of brazing. Upon sintering, the metal is heated to the molecular stirring point and diffuses into adjacent metals over a relatively long period of time to form metallurgical junctions. Sintering can be used to bond the components of the heat exchanger together to provide brazing to the EBL at lower temperatures.

In an embodiment, the first step of attaching the EBL is to apply a polymer binder to the boiling side of the metal wall. The metal powder, which may include the first metal and the second metal, is then sprinkled onto the plastic binder. The metal wall having the metal powder bounded by the plastic is surrounded by an inert atmosphere such as nitrogen, and the temperature is sufficient to effect metallurgical bonding between the metal powder particles with respect to each other and against the boiling side of the metal wall. Raise to brazing temperature for a time. The plastic binder is decomposed by heat and evaporated. The circulating inert gas reduces oxide film formation and also purifies decomposition gas from the binder material. The bonded metal powder forms a highly porous three dimensional matrix that gives the EBL a nuclear boiling site.

Suitable plastic binders include polyisobutylene, polymethylcellulose commercially available as METHOCEL with a viscosity of at least 4000 cps, and polystyrene having a molecular weight of 90,000. The binder can be dissolved in a suitable solvent such as kerosene or carbon tetrachloride for polyisobutylene and polymethylcellulose binders, xylene or toluene for polystyrene binders. The boiling side should be cleaned free of grease, oil or oxide to obtain proper bonding of the EBL to this boiling side. Before applying the plastic solution, the boiling side is submerged in the plastic solution to facilitate wetting, thereby achieving a more uniform distribution of the plastic binder. The plastic solution can be applied to the boiling side in such a way as to obtain a uniform layer, for example by spraying, dipping, brushing or paint rolling. After application, the layer is dried in air during or after application of the metal powder to evaporate most of the solvent. The self-supporting solid layer of the metal powder and the binder is left in place on the metal wall by the binder.

The metal powder comprising the first and second metals is mixed with the flux. Upon heating, the flux melts to extract oxides from the metal that can interfere with the bonding of the metal particles to each other and to the boiling side. The flux may be a commercial salt, such as commercially available aluminum potassium fluoride, a mixture of KAlF ₄ and KAlF ₆ . Other fluxes may be appropriate.

The core 20 of the heat exchanger 10 is assembled by stacking layers of components. If brazing of the core 20 is not performed in a vacuum furnace, each component must be covered with flux before lamination. A suitable way to coat the components with the flux component is to mix the flux with the modified alcohol in a 1: 1 volume ratio and brush or spray the flux solution onto the components prior to lamination. The stacking order will be described in terms of those shown in FIGS. 2 and 3. The cap sheet 40 is located at the bottom of the laminated surface with the outer surface of the cap sheet facing down. The brazing foil layer is laminated on at least two vertical edges 48 of the inner surface of the cap sheet 40 or perhaps over the entire inner surface of the cap sheet 40. Vertical spacer bars 42 are stacked on the vertical edges 48 of the inner surface of the cap seat 40. A brazing foil may be provided only at the vertical edges 48 of the cap sheet 40, in which case only the vertical spacer bar 42 is in the inner surface of the cap sheet 40 forming the boiling passage 12. Because it is brazed. Typically, the horizontal spacer bar 60 is not stacked in the boiling passage 12. However, in the embodiment, if the cap sheet 40 forms the cooling passages 14, the horizontal spacer bar 60 must be laminated to the cap sheet 40 and brazed. A brazing foil layer is stacked on top of the vertical spacer bar 42. Directly above the vertical spacer bar 42 may be a strip of brazing foil. On the top of the vertical spacer bar 42 is a metal wall 44 with an EBL 46 on the boiling side 44a facing downwards towards the cap seat 40 and a cooling side 44b facing upwards. Are stacked. The vertical edge 48 of the boiling side 44a without EBL 46 is seated on the brazing foil at the top of the vertical spacer bar 42. The brazing foil layer lies on top of the cooling side 44b of the metal wall 44. A primary pin stock 54 comprising a primary pin 52, a distribution pin stock 58 including a distribution pin 56, a collection pin stock 68 including a collection pin 66, and a horizontal spacer. Bar 60 and vertical spacer bar 42 are all stacked on top of the brazing foil layer overlying the cooling side 44b of metal wall 44. The brazing foil layer rests on the primary pin stock 54, the distribution pin stock 58, the collection pin stock 68 including the collection pin 66, and the spacer bars 42, 60. Next, another metal wall 44 having a cooling side 44b facing downward and a boiling side 44a facing upward is placed on the brazing foil layer. At the top of the metal wall 44 a strip of brazing foil lies just inside the vertical edge 48 of the boiling side 44a outside the EBL 46. The vertical spacer bar 42 lies on top of the strip of the brazing foil inside the vertical edge 48. On top of the vertical spacer bar 42 lies a strip of brazing foil. An additional metal wall 44 with downwardly facing boiling side 44a is stacked on top with a vertical edge 48 that mates with a strip of brazing material on top of the vertical spacer bar 42. The remainder of the core 20 of the heat exchanger 10 is stacked as described above until the cap sheet 40 is stacked on top of the stack. Both sides of the primary fin stock 54, the spacer bars 42, 60 and / or the cooling side 44b of the metal wall 44 may be integrally covered with the brazing material layer. This eliminates the need to add a brazing foil layer in the stack that makes up the core 20. However, if the pin stock 54, 58, 68 and / or spacer bars 42, 60 can be achieved to be coated with brazed material on both sides, the use of the brazing foil can be avoided.

After the core 20 is completely stacked, the core is inserted into a furnace having an inert gas atmosphere and heated to raise the center temperature of the core 20. After maintaining at elevated temperature for a period of time, the core is allowed to cool. The elevated temperature is above the melting temperature of the brazing material and below the melting temperature of the EBL 46 material and the melting temperature of the base metal upon application. In an embodiment, the elevated temperature may be below the melting temperature of the EBL 46 material after application. In a controlled atmosphere brazing environment, aluminum alloy 4047 may be used as the brazing material, in which case the elevated brazing temperature is about 607 ° C. to 618 ° C. (1125 ° F. to 1145 ° F.). The aluminum alloy designations provided herein are in accordance with conventional alloys used by those skilled in the art of aluminum brazing. The brazing material melts to form a metallurgical bond with adjacent metal members, thereby providing a robust metal heat exchanger core. EBL 46 maintains highly porous structural integrity. The remaining flux on the surface of the core 20 can be maintained but will be cleaned without affecting normal operation.

After brazing the cores 20 together, the manifolds 18, 28 and headers 22, 30 are welded to the core 20 as shown in the embodiment of FIG. 1. Conduits 16, 24, 26, 32 are all secured to appropriate manifolds 18, 28 or headers 22, 30. Conveying, dispensing, collecting and retrieving equipment other than that shown in the embodiment of FIG. 1 may be used within the scope of the present invention.

Alternatively, one or both of the brazing steps may take place in a vacuum oven. No flux is required and usually lower temperatures are used for brazing. However, in the vacuum brazing process, it takes longer for the core to reach the brazing temperature, after which cooling is allowed. If the stacked cores are brazed in a vacuum environment, aluminum alloy 4104 may be used as the brazing material, in which case the elevated brazing temperature is about 582 ° C to 593 ° C (1080 ° F to 1100 ° F).

For the present invention, it is important that the EBL can withstand the final brazing heat treatment. In a brazing aluminum heat exchanger, the brazing material, whether powder, foil or cladding, may comprise a eutectic alloy of at least 80 wt% aluminum and 10 to 15 wt% silicon. In an embodiment, the eutectic alloy comprises 11-13 weight percent silicon and at least 85 weight percent aluminum. In another embodiment, the brazing eutectic alloy is aluminum alloy 4047 and may comprise 12 wt% silicon and 88 wt% aluminum. Other components of the core 20, such as walls, pin stock and spacer bars, may comprise aluminum alloy 3003 consisting of a highly matched aluminum alloy of 98 wt% aluminum and 2 wt% manganese. Aluminum alloy 3003 may also contain small amounts of magnesium and iron. The term "highly balanced" means greater than 90% by weight. Other components may be suitable, including near pure aluminum or highly matched aluminum alloys. In vacuum brazing applications, a highly harmonized aluminum alloy may be provided with 1-2 weight percent magnesium. The materials that make up the EBL may include 0.5-1.5 wt.% Of silicon and at least 95 wt.% Of nearly pure aluminum or a highly matched aluminum alloy. In an embodiment, the EBL may comprise 5-11 wt% brazing material and at least 85 wt% of nearly pure aluminum or a highly matched aluminum alloy. In an embodiment, the EBL comprises a eutectic alloy comprising at least 90% by weight pure or highly matched aluminum and 11-13% by weight silicon and at least 85% by weight aluminum. In an embodiment, the eutectic alloy in powder form is mixed with nearly pure or highly matched aluminum in powder form. In order to prevent oxidation of aluminum in non-vacuum brazing ovens, flux comprising 5 to 10% by weight of powdered mineral salts should be included in the EBL material upon application.

Without wishing to be bound by any particular theory, the aforementioned powdered EBL material mixture, the brazing eutectic alloy powder, is melted to form an alloy by wetting solid aluminum powder that is substantially unmelted. After application, the resulting EBL melts at a higher temperature than the brazing eutectic alloy due to the lower concentration of silicon metal in the aluminum alloy. At this time, the EBL can withstand the brazing temperatures associated with the bonding of the laminated heat exchanger core dangerously close to the temperature at which the EBL material is initially brazed without loss of performance.

In the case of sintering EBL, pure aluminum alloy 3003 powder can be sintered at 1185 ° F. (641 ° C.). Using a brazing foil made of a eutectic alloy of silicon and aluminum described above, a brazing temperature of 604 ° C. to 613 ° C. (1120 ° F. to 1135 ° F.) under controlled inert atmosphere, and 566 ° C. to 596 ° C. (1050 ° F. to 1050 ° C.) in a vacuum environment. The cores can be bonded together at a brazing temperature of 1105 ° F.).

Example I

83.6% by weight of aluminum alloy 3003 powder, 8.4% by weight of brazing flux comprising potassium aluminum fluoride, and 8.0% by weight of aluminum alloy 4047 brazing powder were mixed to obtain a reinforced boiling powder. An adhesive comprising 38% by weight of polyisobutylene and 62% by weight of VARSOL light kerosene solvent, sold by Clifton Adhesives as CS-200 A3, was mixed and brushed on three tube walls of aluminum alloy 3003. The enhanced boiling powder was then sprayed onto the adhesive and heated under nitrogen atmosphere in a small furnace. Each coated tube wall was heated to 621 ° C. (1150 ° F.) for 9 minutes. The adhesive and solvent were evaporated, leaving EBLs between 0.3 and 0.4 mm (10 to 15 mils) thick. The resulting EBL had a highly porous structure and was determined to have a boiling heat transfer coefficient of at least 204,418 kJ / hr / m ² K (10,000 BTU / hr / ft ² ° F).

Example II

Two metal tube walls were coated with adhesive and reinforced boiling powder as described in Example 1. Each tube wall was heated to a brazing temperature of 623 ° C. (1153 ° F.) and then cooled in a controlled nitrogen atmosphere in an approximately atmospheric pressure closed distiller.

The first metal tube wall was heated and cooled over a period of 48 minutes. As a result of testing the first metal tube wall, it was determined to have a heat transfer coefficient of at least 204,418 KJ / hr / m ² K (10,000 BTU / hr / ft ² ° F), which is more than suitable for surfaces with EBL. The first metal tube wall was then sent to a second furnace to simulate the vacuum brazing of the entire heat exchanger core by heating the tube wall to a temperature of 593 ° C. (1100 ° F.) and leaving it to that temperature for 24 hours before cooling. . Visual inspection showed that the quality of the EBL was not affected. The first metal tube wall was tested again and determined to have a heat transfer coefficient of at least 204,418 KJ / hr / m ² K (10,000 BTU / hr / ft ² ° F).

The second metal tube wall was heated and cooled over a period of 36 minutes. As a result of testing the second metal tube wall, it was determined to have a heat transfer coefficient of at least 204,418 KJ / hr / m ² K (10,000 BTU / hr / ft ² ° F), which is more than suitable for surfaces with EBL. The second metal tube wall is then sent to a second furnace to heat the tube wall to a temperature of 613 [deg.] C. (1135 [deg.] F.) and leave it at that temperature for 2 hours in an atmospheric nitrogen atmosphere before cooling to control the entire heat exchanger core. Brazing under simulated atmosphere was simulated. Visual inspection showed that the quality of the EBL was not affected. The second metal tube wall was again tested and found to have a boiling heat transfer coefficient of at least 204,418 KJ / hr / m ² K (10,000 BTU / hr / ft ² ° F). After heating the EBL from the brazing temperature of the EBL to a temperature of 8.3 ° C. (15 ° F.), the structure of the EBL survived heat treatment without significant loss of structure or performance.

Claims (10)

In the heat exchanger (10), A plurality of metal walls 44 each having two sides, a boiling side 44a and a cooling side 44b, the boiling side having a porous reinforced boiling layer 46, the boiling layers being together A brazing thermally conductive particles integrally bonded and metallurgically bonded to the boiling side, the boiling side of the plurality of metal walls forming a boiling passage 12 and the cooling side of the plurality of metal walls being a cooling passage 14 A plurality of metal walls each of which further comprises a joining surface 48; A spacer member 42 that separates the metal wall 44 from each other, A metal layer located between the junction surface 48 of the metal wall 44 and the spacer member 42 in the heat exchanger 10 and having a melting temperature lower than the melting temperature of the enhanced boiling layer 46; A boiling inlet 51 carrying liquid to the boiling passage 12; A cooling inlet 50 for conveying fluid into the cooling passage 14; A boiling outlet 49 for recovering steam from the boiling passage 12; A cooling outlet 64 for recovering fluid from the cooling passage 14 Heat exchanger comprising a. The heat exchanger of claim 1, wherein the metal wall 44 comprises aluminum. The heat exchanger of claim 1 or 2, wherein the thermally conductive particles comprise aluminum. 3. Heat exchanger according to claim 1 or 2, wherein the reinforced boiling layer (46) comprises 0.5 to 1.5 wt% silicon. 3. The reinforced boiling layer 46 according to claim 1 or 2, wherein the enhanced boiling layer 46 comprises an alloy powder, the alloy powder being mixed with a eutectic alloy of at least 85% by weight of aluminum and 11 to 13% by weight of silicon. A heat exchanger comprising more than 90% by weight of aluminum. 6. The heat exchanger of claim 5, wherein the alloy powder constitutes 92% by weight of the reinforced boiling layer (46) and the eutectic alloy constitutes 8% by weight of the reinforced boiling layer (46). 3. The heat exchanger of claim 1 or 2, wherein the boiling side (44a) has a boiling heat transfer coefficient of at least 204,418 kJ / hr / m ² / K. 6. The heat exchanger of claim 5, wherein the eutectic alloy is 12 wt% silicon and 88 wt% aluminum. delete As a manufacturing method of the heat exchanger 10, Providing a plurality of metal walls 44 having a boiling side 44a, a cooling side 44b, and one or more joining surfaces 48, Attaching thermally conductive particles to the boiling side 44a of the plurality of metal walls 44; The metal wall 44 to which the thermally conductive particles are attached is heated to a first temperature to integrally bond the thermally conductive particles together, and the thermally conductive particles are metallurgically bonded to the metal walls by brazing to form a porous reinforced boiling layer ( 46), The spacer member 42 is assembled to the plurality of metal walls 44 so that the boiling side 44a of the plurality of metal walls forms the boiling passage 12 and the cooling side 44b of the plurality of metal walls Providing a cooling passage 14 and providing a metal layer between the joining surface 48 of the metal wall and an adjacent surface of the spacer member 42; The assembly is heated to a second temperature lower than the first temperature such that the metal layer is at least one of the adjacent surface of the spacer member 42 and the adhesive surface 48 of the metal wall 44 while maintaining the porosity of the enhanced boiling layer. Splicing to Method of manufacturing a heat exchanger comprising a.

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